Fluid coking-steam cracking combination process

ABSTRACT

THIS INVENTION RELATES TO A FLUID COKING-STEAM CRACKING FURNACE PROCESS COMBINATION FOR PRODUCING COKE AND GASEOUS HYDROCARBONS FROM A HEAVY HYDROCARBON FEEDSTOCK WHEREIN THE HEAT REQUIREMENTS FROM THE ENDOTHERMICCRACKING REACTION IN THE FLUID COKING VESSEL ARE SUPPLIED DIRECTLY TO THE FLUIDIZED BED OF HOT CARBONACEOUS PARTICLES. IN ONE EMBODIMENT, STEAM IS HEATED IN A FURNACE, PREFERABLY A STEAM CRACKING FURNACE, AND IS THEREAFTER PASSED INTO THE FLUID BED TO SUPPLY ALL OR ESSENTIALLY ALL THE HEAT REQUIREMENTS FOR THE CRACKING, I.E. COKING REACTION IN THE FLUID BED. IN ANOTHER EMBODIMENT, STEAM IS FIRST HEATED IN A FURNACE, PREFERABLY A STEAM CRACKING FURNACE. THEREAFTER, SUITABLE OXYGEN-CONTAINING COMBUSTION GAS MIXTURES, E.G. HYDROGEN-OXYGEN ARE EMPLOYED TO SUPPLY THE REMAINING PORTION OF THE HEAT REQUIRED TO RAISE THE TEMPERATURE OF THE STEAM SUCH THAT THE STEAM, WHEN INTRODUCED DIRECTLY INTO THE BOTTOM OF THE FLUID BED, IN ADDITION TO FLUIDIZING THE BED, SUPPLIES THE HEAT REQUIREMENTS FOR THE COKING REACTION. IN STILL ANOTHER EMBODIMENT, THE COMBUSTION PRODUCTS FROM SUITABLE OXYGEN-CONTAINING COMBUSTION-GAS MIXTURE, IE.E NATURAL GAS AND OXYGEN, ARE INJECTED DIRECTLY INTO THE UPPER PORTION OF FLUID BED SUCH THAT THE INJECTION OF THE COMBUSTION PRODUCTS AND STEAM FROM A STEAM CRACKING FURNACE INTO THE FLUID BED SUPPLY THE HEAT REQUIREMENT FOR THE COKING REACTION DIRECTLY TO THE BED. ADDITIONALLY, THE INTRODUCTION OF STEAM DIRECTLY INTO THE FLUID BED PROVIDES THE CARRYING AND CRACKING MEDIUM FOR THE VAPORIZED HYDROCARBONS RECOVERED FROM THE FLUID BED COKING ZONE, WHICH VAPORIZED HYDROCARBONSTEAM MIXTURE IS THEN PASSED THROUGH A STEAM CRACKING FURNACE TO PRODUCE LOW MOLECULAR WEIGHT UNSATURATED PRODUCTS.

PROCFSS May 9, 1972 G, w T ETAL PLUM) COKING-STEAM CRACKING COMBINATION Filed Sept. 19. 1969 PRODUCT Fig. 3

Fig. 2

6 B WIN/1 6,5 Jg/m/ INVENTORS ATTORNEY BY [J r) United States Patent Office 3,661,767 Patented May 9, 1972 US. Cl. 208-54 27 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a fluid coking-steam cracking furnace process combination for producing coke and gaseous hydrocarbons from a heavy hydrocarbon feedstock wherein the heat requirements for the endothermiccracking reaction in the fluid coking vessel are supplied directly to the fluidized bed of hot carbonaceous particles. In one embodiment, steam is heated in a furnace, preferably a steam cracking furnace, and is thereafter passed into the fluid bed to supply all or essentially all the heat requirements for the cracking, i.e. coking reaction in the fluid bed. In another embodiment, steam is first heated in a furnace, preferably a steam cracking furnace. Thereafter, suitable oxygen-containing combustion gas mixtures, e.g. hydrogen-oxygen are employed to supply the remaining portion of the heat required to raise the temperature of the steam such that the steam, when introduced directly into the bottom of the fluid bed, in addition to fluidizing the bed, supplies the heat requirements for the coking reaction. In still another embodiment, the combustion products from suitable oxygen-containing combustion-gas mixtures, i.e. natural gas and oxygen, are injected directly into the upper portion of fluid bed such that the injection of the combustion products and steam from a steam cracking furnace into the fluid bed supply the heat requirement for the coking reaction directly to the bed. Additionally, the introduction of steam directly into the fluid bed provides the carrying and cracking medium for the vaporized hydrocarbons recovered from the fluid bed coking zone, which vaporized hydrocarbonsteam mixture is then passed through a steam cracking furnace to produce low molecular weight unsaturated products.

BACKGROUND OF THE INVENTION This invention relates to an improved fluid cokingsteam cracking furnace process combination for the thermal cracking of a heavy hydrocarbon feedstock and residual feeds which comprises introducing the feedstock into a fluidized bed of hot carbonaceous particles to form carbonaceous materials, i.e., coke, hydrogen and gaseous hydrcarbon products. More particularly, this invention relates to a fluid coking-steam cracking combination process wherein the heat requirements for the endothermic cracking reaction of the heavy hydrocarbon feedstock in the fluid bed are supplied directly to the fluidized bed of hot carbonaceous particles without the necessity of transferring coke particles to a separate vessel. On one embodiment, steam is heated in a furnace, preferably a steam cracking furnace, and is thereafter passed into the fluid bed to supply all or essentially all the heat requirements for the cracking, i.e. coking reaction in the fluid bed. In another embodiment, steam is heated in a steam cracking furnace and thereafter suitable oxygen-containing combustion gas mixtures, e.g. hydrogen-oxygen, are employed to supply the remaining portion of the heat required to raise the temperature of the steam such that the steam, when introduced directly into the bottom of the fluid bed, in addition to fluidizing the bed, supplies all or essentially all the heat requirements for the coking reaction. In still another embodiment, the combustion products from suitable oxygen-containing combustion gas mixtures, i.e. natural gas and oxygen are injected directly into the upper portion of fluid bed. The introduction of such combustion products along with the introduction of steam from a steam cracking furnace to the bottom of the bed, supplies all or essentially all of the heat requirement for the coking reaction directly to the bed. Additionally, the introduction of steam directly into the fluid bed also provides the carrying and cracking medium for the vaporized hydrocarbons recovered from the fluid bed coking zone, which vaporized hydrocarbon-steam mixture is then passed through a steam cracking furnace to produce low molecular weight unsaturated products.

DESCRIPTION OF THE PRIOR ART It is well known in the art to prepare coke and gaseous products in a fluidized process at temperatures between about 800 and 2800 F. In a typical fluid coking process, a hydrocarbon feed is injected into a reactor containing a hot fluidized bed of coke particles. The hydrocarbon is cracked to form solid coke which deposits on the existing coke particles, enlarging them in size. To maintain the desired particle size in the bed, smaller seed coke is added which may be obtained by comminuting part of the product coke, or steam jet attriters can be employed in the coker. Vapors containing partially cracked hydrocarbons and hydrogen are also liberated. Heat for the endothermic cracking reactions is supplied by circulating coke particles from the reactor through an external heater or burner vessel wherein they are heated to a temperature generally ranging from about to 400 F. above the temperature in the cracking zone and thereafter returned to the fluid bed of the reactor.

Circulation of coke particles through an external burner presents numerous problems. As the reaction involved in the instant process is an endothermic one, a major problem involves that of supplying heat for the cracking, i.e., coking, reaction. To accomplish this end, a burner vessel is generally employed in combination with the primary re-' action, i.e. coker vessel. The particulate coke solids, generally in fluidized phase, are circulated between the bed of the primary reaction vessel and the heater where the coke is heated and then retransferred or recycled to the bed of the reactor to impart heat for continuation of the coking reactions. The heat is generally supplied by burning oxygen or an oxygen-containing gas (air) and coke as fuel in the heater to which the coke is circulated. The combustion imparts heat to the coke particles, elevating the temperature of the coke above that of the reaction bed, so that heat is transferred to the primary reactor by recycle thereto of the heated coke particles.

A major deficiency associated with such a process is that serious pollution and heat inefliciencies occur if the combustion gases are vented directly to the atmosphere. Expensive elements are generally required to remove heat and pollutants from the combustion products. Furthermore, because of the high particle velocity to the various transfer lines between vessels, excessive wear is often encountered. Moreover, the unit downtime in a fluidized solids process generally varies substantially as the number of elements in the apparatus. In addition, in a conventional coking system described above, the burner vessel must be operated at a correspondingly high pressure, resulting in high cost for compressing the combustion air.

SUMMARY OF THE INVENTION It has now been discovered that improved thermal efficiency and reduced coke consumption can be realized in a fluid coking operation by combining said fluid coking operation with a steam cracking furnace such that steam,

having first been heated in a cracking furnace, is supplied directly to the fluid bed to: (a) supply the heat requirements directly to the cracking zone; (b) fluidize the bed of hot carbonaceous particles and provide diluent steam, i.e. the carrying and cracking medium for the vaporized hydrocarbons recovered from the cracking zone which are subsequently passed through the convection and radiant sections of a steam-cracking furnace to produce low molecular weight unsaturated hydrocarbon products.

In one embodiment of the instant invention, steam is first passed through a furnace, preferably through a steam cracking furnace, to heat the temperature of the steam to a point suflicient, i.e. from about 1200 to about 1900 R, such that the steam, when passed from the furnace to the fluid bed of the coker vessel, supplies the heat required for the coking reaction. In another embodiment of this invention, steam is first passed through a furnace to heat the steam to a temperature in the range of from about 1200" to about 1900 F., and more preferably from 1400 to 1600 F. Thereafter, suitable oxygen-containing combustion gas mixtures such as hydrogen and oxygen or natural gas and oxygen are employed as burners to supply the remaining portion of the heat required to raise the temperature of the steam to a range of from about 1900 to about 3200" F. and more preferably from 2200 to 2700" F., such that the fluid bed system is maintained in a heat balance of from about 800 to about 1100 F. and preferably from 900 to 1000 F.

In still another embodiment, suitable combustion gases such as natural gas or refinery gases are burned with oxygen and the hot combustion products from such a burner are injected directly into the fluid coke bed within two feet of the surface of the bed. The hot combustion productsare injected within the upper two feet of the surface of the bed to provide sufficient contact time to heat the coke while substantially precluding the reaction of combustion gases with the coke to form excessive amounts of carbon monoxide, which would result in a thermally inefiicient process. The injection of these combustion gases, along with the introduction of steam from a steam cracking furnace as described above, supplies the heat requirements for the coking reactions directly to the bed.

It is to be understood that the introduction of steam directly into the fluid bed supplies all of the diluent steam required for the subsequent steam cracking of the gaseous hydrocarbons recovered from the coking zone such that no additional source of super-heated steam need be employed to carry and act as a cracking medium for the vaporized hydrocarbons recovered from the fluid bed coking zone. The amount of steam in the vapors leaving the coking zone is in the range of from about to about 55 wt. percent, and more preferably from about to about wt. percent.

As previously mentioned, vaporized hydrocarbons along with steam are recovered from the cracking zone and are passed directly to a steam cracking furnace. The vaporized hydrocarbons and steam are first heated in the convection section of a steam cracking furnace to a temperature in therange of from about 900 to 1300 F. Thereafter, the products from the cracking zone are passed to the radiant zone of a steam cracking furnace Where the steam cracking reaction occurs. Here the products in the radiant section are heated to a temperature of from about 1300 to about 1600 F. The residence time in the cracking zone ranges from about .02 to 1.0 second, preferably 013 to 0.7 second, the higher the temperature, the lower the residence time to obtain a given conversion level. Pressures within the tubes are not critical to the process and can range from about 5 to about 20 p.s.i.g. at the coil outlet, but higher pressures, e.g. up to p.s.i.g. at the coil outlet can be tolerated at some sacrifice in olefin yield. In order to optimize the yield of low molecular weight unsaturated hydrocarbon products, low hydrocarbon partial pressures are desirable. Steam, which is recovered from the cracking zone of the fluid bed coker 4 along with vaporized hydrocarbons, is an effective diluent for this purpose such that vaporized hydrocarbon feed which is fed to the steam cracking furnace is comprised of from about 10 to 50 wt. percent steam and more preferably 25 to 40 wt. percent steam.

In accordance with the practice of the instant invention, a heavy hydrocarbon feedstock is introduced into the upper portion, i.e., scrubber section, of a coker vessel. The feed may be introduced at ambient tempertature or may first be preheated to a temperature in the range of from about 500 to about 900 F. and more preferably 700 to 800 F. by passing the feed through a furnace, more preferably through the convection section of a steamcracking furnace. Exemplary hydrocarbon feeds which can be employed in the practices of this invention include, but are not limited to, heavy hydrocarbon oils such as atmospheric and vacuum still crude residua, whole crude, tars and pitches. Typically, the residua feeds have an initial boiling point of about 600 F., although they may have a boiling point as high as above about 900 F., and an API gravity of about 0 to 20, and a Conradson carbon content of about 3 to 40 weight percent. The amount of coke formed depends on the character of the materials being processed and, to some extent, upon the coking conditions. In the case of high Conradson carbon residuum feedstock, the coke yield can be 50 weight percent or higher based on the residuum.

The lower boiling components of the hydrocarbon feed which are introduced into the upper portion, i.e., scrubber section, of the coker vessel are vaporized by the gases passing upwardly from the fluidized bed of hot carbonaceous particles such that the product vapors which pass overhead from the coker vessel contain steam, the light fractions of the feed together with the lighter portions of the gaseous vapors passing upwardly from the fluidized bed. The light hydrocarbon fractions passing overhead contain cracked products such as ethylene and other hydrocarbon vapors, exemplified by the components of a light naphtha and gas oil fraction. These light fractions, along with steam are passed directly to the furnace of a steam cracking unit where they are further cracked to form valuable low molecular weight unsaturated hydrocarbons comprising e.g. about 45 wt. percent C and about 16.5 wt. percent ethylene based on total hydrocarbon feed passed to the steam cracking unit, which products are then further processed for the recovery of the desired products. The heavy, unvaporized fractions of the initial hydrocarbon feed, along with the heavy condensed components of the vapors from the fluidized bed fall to the bottom of the scrubber, which serves to remove coke particles from the vapors going to the steam cracking furnace, and the liquid fractions may then be fed through the convection section of the steam cracking unit before being passed to the fluid bed coking zone. When the liquid fractions are first heated by passing through the convection section of a steam cracking unit, which section is usually at a temperature in the range of from about 500 to about 900 F., the preheated liquid portions may supply a very minor portion of the heat requirement to the coking zone when the temperature of the liquid fractions entering the coking zone is above that at which the coking operation is being conducted. When this alternative embodiment is employed, it is to be understood that the steam, either alone or supplemented by combustion gas burners as described above, will supply at least of the process heat requirement to the coking vessel. More preferably, when this embodiment of preheating the liquid fractions is employed in conjunction with the preferred coking temperature of the instant process, it is seen that the steam either alone or supplemented with the combustion gas burner supplies essentially all, i.e. above 80+ percent or all of the process heat requirement to the coking zone.

The vaporized products liberated'in the coking zone by the thermal cracking process pass upwardly from the bed through a cyclone and into the scrubber section, i.e., upper portion, of the coker vessel. Cyclone separators are a well-known means for separating gases and solids from gas-solid suspensions. The coke-laden gases pass upwardly from the coking zone into a cyclone separator, separating nearly all of the coke particles which then pass as a dense phase to a standpipe or dipleg from the bottom of the cyclone back into the fluid bed of the cracking reactor. The gases leave the top of the cyclone at high temperatures and function in the instant process to vaporize the light ends of the hydrocarbon feed which has been introduced into the scrubber section as described above.

The heat for carrying out the endothermic coking reaction is, in accordance with the instant invention, generated in an integrated furnace, preferably a steam cracking unit and may be supplemented by combustion gas burners. As described above, steam is first heated in a furnace, preferably a steam cracking furnace to a temperature in the range of from about l200 to about 1900 F. Thereafter, the heat required to maintain the fluid bed in heat balance at about 700 to about 1100 F. and more preferably from about 900 to about 1000" F., is supplied either by: (a) introducing the steam from the furnace to supply the heat requirements directly to the fluid bed, (b) employing a hydrogen-oxygen or other suitable combustion gas burner to further heat the steam to a temperature of from about 2000 to about 3200 R, such that the steam fed at such a temperature directly to the fluid bed supplies the heat requirements for the cracking reaction, or (c) introducing steam from the furnace directly into bottom of the fluid bed and further heating the bed by injecting combustion products from a burner, which burns an oxygen-containing gas and a fuel, such as natural gas, directly into the fluid bed at a point within the upper two feet of the surface of the bed. When embodiment (a) is employed, the amount of heat expressed in B.t.u.s supplied by the steam from the furnace to the cracking Zone is 100%. When either embodiment (b) or (c) is employed to supply the heat requirements to the fluid bed, the amount of heat expressed in B.t.u.s supplied by the steam from the steam cracking furnace is in the range of from about 20 to about 80%, more preferably from about 40 to 60% of the process heat required to maintain the heat balance required in a fluid coker.

The amount of steam which is introduced into the bottom of fluid bed, in accordance with the instant invention, is in the range of from about 0.1 to about 1.0 and more preferably from about 0.3 to 0.6 pound of steam per pound of feedstock on a coke free basis. In introducing said amount of steam into the bottom of the fluid bed in embodiment (b) of this invention, about 75 to 95 and more preferably from about 85 to 90 wt. percent of the steam has been heated in the steam cracking furnace, or in a separate furnace or other heating system.

When the heat requirements for the coking reaction are supplied by steam and by injecting the combustion products of a combustion gas burner such as natural gas and oxygen directly to the fluid bed as in embodiment (c) of this invention; about 0.005 to 0.05 and more preferably from about 0.01 and 0.02 pound of natural gas and about 0.02 to 0.2 and more preferably from about 0.04 to 0.08 pound of oxygen are employed in the combustion gas burners per pound of feedstock. The pressures at which said combustion products are injected into the bed is in the range of from about 20 to 200 and more preferably from about 50 to 100 p.s.i.g.

The pressure at which the steam which has passed through a furnace is introduced into the coker vessel is in the range of from about 60 to about 200+ p.s.i.a. and more preferably from about 75 to about 150 p.s.i.a. The above-described conditions are such as to substantially convert the hydrocarbon feedstock into vaporized hydrocarbons and carbonaceous material.

Preferably, this steam is introduced below the fluidized bed in the conical shaped portion of the coker vessel. The

conical shaped portion of the coker vessel is refractory lined and agrid of refractory or metal separates the fluidized bed from the conical portion of the reactor vessel. The grid allows a uniform flow of steam from the bottom of the coker vessel to produce uniform agitation and fluidization of the coke particles. A standpipe protrudes through the grid into the fluid coking portion of the reactor vessel and extends outwardly down through the conical portion of the reactor vessel through which coke is removed from the vessel.

The coke which is removed through the standpipe as described above is passed into a calciner to form the product coke. The calciner also contains a fluidized bed of carbonaceous particles into which the coke from the coker vessel passes. The bed of carbonaceous particles, i.e. coke, in the calciner is fluidized and heated by burning an oxygen-containing gas with a fuel, i.e. natural gas in a burner, which hot combustion products are injected within the upper two feed of the bed. This calciner bed is operated at a temperature from about 2000 to 2600 F., preferably from about 2300 to about 2400 F. and serves to remove volatiles from the coke. At the same time the density and electrical conductivity of the carbonaceous particles increase markedly, making the coke suitable as a raw material for making electrodes such as are used in electric furnaces and in electrolytic production of aluminum. The coke is held at calcining temperature for from about one-quarter to about 2 hours.

The calcined coke product is withdrawn through a standpipe which communicates with the bed of fluidized coke particles. The gases from the fluidized bed of the calciner pass through a cyclone, similar to that described above for the fluid coker, and overhead from the calciner to a heat exchanger and ultimately into a separator where the flue gas and volatiles from the coke are separated from the coke fines and water.

In another embodiment of this invention, the coke passing from the coker vessel is introduced into a fluidized bed of carbonaceous particles in the calciner as described above. In this embodiment, the coke product is withdrawn through a standpipe from the fluidized bed, contacted for a short time with hot steam which has passed through a steam cracking furnace and further heated with hydrogen-oxygen burners as described above for the coker vessel to increase the temperature of the steam to a range of from about 2l00 to 3200 F. in order to heat the coke particles to a temperature equal to or above that temperature existing in the fluid calciner bed, e.g. 2000 to about 2600 F. These coke particles are then recycled into the upper portion of the calciner and pass through a cyclone such that the hot steam and volatiles from the coke may be recycled into the fluidized bed of the coker vessel where some of their heat content is used to supply a portion of the heat requirements of the coker, while the the coke then is returned to the calciner. The coke product is removed from the standpipe emanating from the bottom of the calciner before said coke particles are contacted with steam in the presence of the hydrogenoxygen burners. The contact time of the coke with steam is held to no more than from about .2 to about 2 seconds, so that undesirable reactions are minimized.

The invention will be more clearly understood by reference to the accompanying drawings wherein:

FIG. 1 shows a suitable method and apparatus for first coking a residual feed in a coker vessel and then cracking the resulting vapors in an integrated steam cracking unit;

'FIG. 2 shows a calciner through which the coke particles from the coker vessel are passed to form the calcined product coke; and

FIG. 3 shows a modification of the calciner wherein the coke is contacted with hot steam from an integrated steam cracker such that the volatiles from the coke may be recycled directly back to the fluid bed coker vessel.

Referring first to FIG. 1, a heavy hydrocarbon feedstock such as an atmospheric residuum is fed through an inlet line 1 into the upper portion, i.e., scrubber section 2 of the coker vessel 3. The coker vessel may be operated at or near atmospheric pressure but is preferably at a moderate pressure of from about 20 to about 100 p.s.i.g. The hydrocarbon feed is contacted in the scrubber section with vapors passing upwardly from the fluidized bed of coke particles 4 through cyclone 5. The vapor contacts the hydrocarbon feed in the scrubber section 2, such that the light fractions of the hydrocarbon feed are vaporized and are passed overhead product 6 along with steam and the light gases from the fluidized bed to the steam cracking furnace 7 which is operated at a temperature above about .1200 F. The steam cracked product is removed from the steam cracking unit, quenched 8, and is subsequently recovered.

The heavy portion of the hydrocarbon feed which is not vaporized falls to the bottom of the scrubber section of the coker vessel along with the heavy condensed fractions of the vapors from the fluidized bed. These heavy fractions may then be removed by way of line 9, passing to a pump 11 which supplies suitable pressure to pass it through line 12 to the fluidized bed portion 4 of the coker vessel. Alter natively, pump 11 may supply suitable pressure to pump the heavy ends settling at the bottom portion of the scrubber section to line 13 to the convection section of the steam cracker 14. The temperature at which the heavy fractions leave the scrubber section are in the range of from about 600 to about 800 F. After passing through the convection section of the steam cracker 14, the heavy ends are returned to the fluidized bed 4 by way of line 15 at a temperature up to about 950 F.

Steam is passed by way of line 16 through the radiant section 17 of a steam cracker. After the steam has been heated in the steam cracking furnace 7, it is passed along line 18 to hydrogen-oxygen bumers 23 and 24 to heat the steam to a temperature in the range of from about 2000 to about 3200 F. The steam is then introduced into the bottom portion 19 of the coker vessel and passes upwardly through the grid 20 to uniformly fluidize the bed, provide diluent steam for the subsequent cracking of the overhead product 6 in the steam cracking furnace, and to supply the heat requirement for the cracking process. The preferred reaction temperature in the coking zone of fluidized bed of coke particles is in the range of about 900 to about 1000" F. A standpipe 21 extends from the fluidized bed portion of the reactor vessel 4 through the conical shaped portion of the vessel 19 and passes outwardly carrying the coke to be calcined by way of line 22.

In FIG. 2, the coke particles passing through line 22 are introduced into a fluidized bed of coke particles 25 in calciner 26. Submerged burners 27 and 28 inject combustion products from an oxygen-containing gas burner, i.e. natural gas-oxygen burner, within one foot of the upper surface of the fluidized coke bed to supply the heat requirements needed for the calciner. The upflowing stream of vapors and carbonaceous solids are passed into a cyclone separator 29. Here the vapors are separated and taken overhead to outlet line 30. The vapors then pass through a heat exchanger 31 and into a separator 32 by way of line 33. The separator, i.e. fractionation zone, causes the flue gas and volatiles from the coke to pass overhead to line 34, whereas the coke fines, Water, etc., are purged through line 35. The calcined product coke is removed from the fluidized bed of coke particles 25 through standpipe 36.

In FIG. 3, an alternative embodiment of calcining the coke removed from the fluid coker 3 by way of line 22 is described. The coke passing from the coker vessel by way of line 22 passes into a fluidized bed of coke 38 in calciner 38. The coke particles are removed from the fluidized bed through line 39 and are contacted with steam passing from a steam cracker furnace (not shown) by way of line 40 and hydrogen and oxygen burners 41 to increase the temperature of the coke particles to about 2400 F. The vapors and solids bearing the coke particles are passed into a cyclone separator 42. Here the vapors including the volatiles from the coke particles and the hot steam are separated and taken overhead by way of line 43 and recycled to the fluidized bed of the coker vessel 4. The calcined coke product is removed by way of line 44.

What is claimed is:

1. In a fluid coking process wherein a heavy hydrocarbon feedstock is cracked in a coking zone containing a fluidized bed of hot carbonaceous particles to produce hydrocarbon vapors and to deposit carbonaceous materials on said particles and wherein the hydrocarbon vapors are recovered from the coking zone and are passed along with diluent steam through a steam cracking furnace to produce low molecular weight unsaturated hydrocarbons, the improvement which comprises introducing steam into the bottom portion of the fluid bed, said steam having previously been heated in a furnace to a temperature sufficient to provide all of the heat requirement for the coking zone directly to the fluid bed and to provide all of the diluent steam for the hydrocarbon vapors recovered from the coking zone which are subsequently passed to the steam cracking furnace.

2. The process of claim 1 wherein said steam is heated to a temperature in the range of from about 1200 to about 1900 F.

3. The process of claim 1 wherein said heavy hydrocarbon feedstock has a boiling point above about 600 F.

4. The process of claim 1 wherein said coking zone is maintained at a temperature in the range of from about 800 to about 1100 F.

5. The process of claim 1 wherein the amount of steam introduced into the bottom of the fluid bed is in the range of from about 0.1 to about 2.0 pounds of steam per pound of feedstock.

6. A process for producing carbonaceous material and low molecular weight unsaturated hydrocarbons which comprises:

(at) introducing a heavy hydrocarbon feedstock into the upper portion of a coker vessel, said coker vessel comprising an upper scrubber zone and a lower coking zone containing a fluid bed of hot carbonaceous particles, and vapor and liquid passages connecting said zones;

(b) introducing steam into the bottom portion of the fluid bed, said steam having previously been heated in a steam cracking furnace in order to supply from about 20 to about of the heat requirements for said coking zone and to supply all of the diluent steam for the subsequent steam cracking operation, and thereafter contacting said steam with a sutficient amount of an oxygen-containing combustion gas mixture to provide the remaining portion of the heat required to raise the temperature of the steam sufficient to provide essentially all of the heat requirements for the coking zone directly to the fluid bed;

(0) recovering as product vapors from the scrubber zone of the coker vessel the light fractions of the vapors passing upwardly from the coking zone, the lower boiling components of said feedstock vaporized in said scrubber zone by contact with said vapors passing upwardly from the coking zone and steam;

(d) passing said product vapors through a steam cracking furnace, said steam cracking furnace operated at a temperature above about 1200 F. to produce low molecular weight unsaturated hydrocarbons;

(e) recovering a liquid from the scrubber zone comprising the unvaporized fractions of the hydrocarbon feedstock and the condensed components of the vapors passing from the coking zone formed in step (c); and

(f) introducing said liquid recovered in step (e) into the coking zone.

7. The process of claim 6 wherein said heavy hydrocarbon feedstock has a boiling point above about 600 F.

8. The process of claim 6 wherein said feedstock is first preheated to a temperature in the range of from about 500 to about 950 F. before being introduced into the upper portion of the coker vessel.

9. The process of claim 6 wherein said steam is heated in the steam cracking furnace to a temperature in the range of from about 1200 to about 1900 F.

10. The process of claim 6 wherein the temperature of the steam introduced into the bottom of the fluid bed is in the range of from about 2000" to about 3200 F.

11. The process of claim 6 wherein the temperature of the coking zone is maintained in the range of from about 700 to about 1100 F.

12. The process of claim 6 wherein the liquid recovered from the scrubber zone is preheated in the steam cracking furnace before being introduced into the cracking zone.

13. The process of claim 6 wherein the oxygen-containing combustion gas mixture consists essentially of hydrogen and oxygen.

14. The process of claim 6 wherein the oxygen-containing combustion gas mixture consists essentially of natural gas and oxygen.

15. The process of claim 6 wherein carbonaceous material is withdrawn from the coking zone and introduced into a calciner, said calciner containing a fluidized bed of hot carbonaceous material, wherein the heat requirements for the fluid bed in the calciner are provided by injecting the combustion products of an oxygen-containing combustion gas burner within one foot of the upper surface of said bed, and withdrawing carbonaceous material from said bed as product coke.

16. The process of claim 6 wherein carbonaceous material is withdrawn from the coking zone and introduced into a calciner containing a fluid bed of hot carbonaceous material, withdrawing the carbonaceous material from said bed and contacting said withdrawn carbonaceous material with a steam, wherein said steam is first heated in a furnace and thereafter contacted with a suflicient amount of an oygen-containing combustion gas mixture to provide the remaining portion of the heat required to raise the temperature of the carbonaceous material to about 2400" F., separating and recovering the vapors resulting from said contact of the carbonaceous materials with the steam and introducing said vapors to the coking zone of the coker vessel.

17. A process for producing carbonaceous material and low molecular weight unsaturated hydrocarbons which comprises:

(a) introducing a heavy hydrocarbon feedstock into the upper portion of a coker vessel, said coker vessel comprising an upper scrubber section and a lower coking section containing a fluid bed of hot carbonaceous particles, and vapor and liquid passages con necting said sections;

(b) introducing steam into the bottom portion of the bed, the said steam having been previously heated in a steam cracking furnace to provide from about 20 to about 80% of the heat requirements for said coking zone and to supply all of the diluent steam for the subsequent steam cracking furnace, and injecting a sufiicient amount of combustion products from an oxygen-containing combustion gas burner within the upper two feet of the surface of the bed, said steam and said combustion products providing essentially all of the heat requirements for the cracking section directly to the fluid bed;

() recovering as product vapors from the scrubber zone of the coker vessel the light fractions of the vapors passing upwardly from the coking zone, the lower boiling components of said feedstock vaporized in said scrubber section by contact with said vapors passing upwardly from the cracking zone and steam;

(d) passing said product vapors through a steam cracking furnace, said steam cracking furnace operated at a temperature above about 1200 F. to produce low molecular weight unsaturated hydrocarbons;

(e) recovering a liquid from the scrubber section comprising the unvaporized fractions of the hydrocarbon feedstock and the condensed components of the vapors passing upwardly from the cracking zone formed in step (c); and

(f) introducing said liquid recovered in step (e) into the cracking zone.

18. The process of claim 17 wherein said heavy hydrocarbon feedstock has a boiling point above about 600 F.

19. The process of claim 17 wherein said feedstock is first preheated in the steam cracking furnace before introduction into the upper portion of the coker vessel.

20. The process of claim 17 wherein said steam is heated in the steam cracking furnace to a temperature in the range of from about 1200 to about 1900 F.

21. The process of claim 17 wherein the temperature of the steam introduced into the bottom of the fluid bed is in the range of from about 2000 to about 3200 F.

22. The process of claim 17 wherein the temperature of the coking zone is maintained in the range of from about 700 to about 1100 F.

23. The process of claim 17 wherein the liquid recovered from the scrubber zone is preheated in the steam cracking furnace before being introduced into the cracking zone.

24. The process of claim 17 wherein the oxygen-containing combustion gas mixture consists essentially of hydrogen and oxygen.

25. The process of claim 17 wherein the oxygen-containing combustion gas mixture consists essentially of natural gas and oxygen.

26. The process of claim 17 wherein carbonaceous material is withdrawn from the coking zone and introduced into 'a calciner, said calciner containing a fluidized bed of hot carbonaceous material, wherein the heat requirements for the fluid bed in the calciner are provided by injecting the combustion products of an oxygen-containing combustion gas burner within one foot of the upper surface of said bed, and withdrawing carbonaceous material from said bed as product coke.

27. The process of claim 17 wherein carbonaceous material is withdrawn from the coking zone and introduced into a calciner containing a fluid bed of hot carbonaceous material, withdrawing the carbonaceous material from said bed and contacting said withdrawn carbonaceous material with steam, wherein said steam is first heated in a steam cracking furnace and thereafter contacted with a suflicient amount of an oxygen-containing combustion gas mixture to provide the remaining portion of the heat required to raise the temperature of the carbonaceous material to about 2400 F., separating and recovering the vapors resulting from said contact of the carbonaceous materials with the steam and introducing said vapors to the coking zone of the coker vessel.

References Cited UNITED STATES PATENTS 2,905,733 9/1959 Boston et al 260-683 2,964,464 12/1960 Smith et a1 208-127 3,090,746 5/1963 Markert et al. 208-127 HERBERT LEVINE, Primary Examiner US. Cl. X.R. 

